1. Field of the Invention
The present invention relates to a multi-channel fluorescence measuring optical system and a multi-channel fluorescence sample analyzer, and more particularly, to a small, cheap multi-channel fluorescence measuring optical system which can rapidly detect fluorescence samples contained in a multi-channel sample holder having several micro-fluidic channels using one optical system, and a multi-channel fluorescence sample analyzer using the optical system.
2. Description of the Related Art
A widely known method of analyzing a sample is to irradiate the sample with a specific wavelength of light and detect the spectrum of light emitted from the sample. For example, DNA concentration is measured by labeling the DNA base with a fluorescent dye and then analyzing the intensity of fluorescence light emitted from the dye.
FIG. 1 illustrates the principle of a sample analyzer which uses general fluorescence analysis. A conventional fluorescence analyzer 100 includes an illuminating unit 110 for irradiating light onto a sample 130, and a detecting unit 120 for detecting fluorescence light emitted from the sample 130. The illuminating unit 110 includes a light source 112, a dichroic mirror 114, and an objective lens 115. The sample 130 is mounted on a sample holder 117. The detecting unit 120 includes a light detector 125, such as a photo multiplier tube (PMT) or photodiode, and a filter 121 for passing only a specific wavelength of light.
The light source 112 can be a halogen lamp, an LED, or a laser. The light emitted from the light source 112 is reflected by the dichroic mirror 114 and strikes the sample 130 on the sample holder 117. The fluorescence light emitted from the sample 130 enters the detecting unit 120 through the dichroic mirror 114. The filter 121 receives the light entering the detecting unit 120 and passes only a specific wavelength, and the light detector 125 detects the intensity of the light from the filter.
Recently, a multi-channel sample analyzer has been developed, to increase the throughput of the sample analysis and rapidly measure the sample. The multi-channel sample analyzer can analyze several samples at once, and can be designed either to simultaneously measure a plurality of samples using a plurality of detecting units, or to sequentially measure a plurality of samples using only one detecting unit.
Apparatuses for simultaneously measuring a plurality of samples using a plurality of detecting units include an apparatus using one detecting unit for each sample (Cepheid Smart Cycler ®), an apparatus in which several samples are simultaneously irradiated by a large one light source, and the fluorescence light emitted from all the samples is measured using one CCD (ABI Prism 7000®, BioRad iCycler®). However, when using as many detecting units as there are samples, the same number of photodetectors, filters, etc., as the samples are required, thereby increasing the volume and the manufacturing cost of the apparatus. Further, when using a CCD detector, only one filter wheel may be used. However, since the highly sensitive CCD needed for fluorescence analysis is expensive, the manufacturing cost of the multi-channel sample analyzer is increased, and thus the analyzer using the CCD detector is not suitable for a small analyzer. Also, in order to perform multi-channel analysis using several wavelengths of light, a rotating filter wheel 143 is generally placed between the sample holder 145 and the CCD 140. However, due to the limit of the frame rate (the number of frame captures per second), the speed of the filter wheel 143 is limited, and thus the time for measuring several wavelengths cannot be further reduced.
Also, the apparatus for sequentially measuring several samples using one detecting unit mounts a plurality of samples on the sample holder and measures the samples by scanning them. The rotating filter wheel is required for multi-color analysis on several wavelengths for one sample, and there is a limit to the multi-channel measuring speed as mentioned above. Also, since the actual measuring time is obtained by multiplying the scanning time of the sample with the filter wheel rotating time, the measuring time is unacceptably long. Also, since a separate device is needed for scanning the samples, the analyzer can not be made small enough.
Particularly, a micro polymerase chain reaction (PCR) using a silicon substrate, which can rapidly control temperature and quickly amplify a very small amount of DNA, can be applied for miniaturization of the PCR equipment, because micro-fluidic channels containing a plurality of samples can be easily formed in a small area of a substrate. However, it is difficult to miniaturize the PCR equipment without miniaturizing the optical system as well. Accordingly, a small optical system must be developed to detect the fluorescence from several micro-fluidic channels.